Tool assembly

ABSTRACT

An improved tool assembly includes a ferroalloy support having an opening formed therein, a ceramic tool element positioned in the opening, and a filler metal containing finely divided refractory hard metal brazed to the support and mechanically bonded to the tool element.

29/473.1 UX 29/473.l X 29/473.1 X

Milch et a1... 10/1970 Stehl et a1.... 12/1955 29/473.l X

6/1939 Pulfrich....................... 11/1938 l-lurley..... 7/1957 Forge, Jr.. 11/1962 Palmour.......

ABSTRACT 8 Claims, 2 Drawing Figures Primary Examinerl.loyd L. King Assistant Examiner-Michael Y. Mar An0meyJames A. Reilly et a1.

An improved tool assembly includes a ferroalloy support having an opening formed therein, a ceramic tool element positioned in the opening, and a filler metal containing finely divided refractory hard metal brazed to the support and mechanically bonded to the tool element.

0 Umted States Patent 11 1 Lock et al.

Everett H. Lock, Houston; Joe K. Heilhecker, Bellaire, both of Tex.

[73] Assignee: Esso Production Research Company,

Houston, Tex.

Apr. 13, 1972 Related US. Application Data [62] Division of Ser. No. 36,834, May 13, 1970, Pat. No.

239/591, 29/473.1 Int. B05b 15/00 239/591, 601, 602; 29/473.l, 489, 472.7; 287/189365 References Cited UNITED STATES PATENTS 5/1964 Rowley et 239/602 X TOOL ASSEMBLY [75] Inventors:

[22] Filed:

[21] Appl. No.: 243,702

[58] Field of PATENTED BEE 4 9 5 4 H W 1 l TOOL ASSEMBLY CROSS REFERENCE TO RELATED APPLICATIONS This is a division of application Ser. No. 36,834, filed May 13, 1970 now US. Pat. No. 3,673,676, issued July 4, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved tool assembly. In one aspect, it relates to an improved nozzle assembly.

2. Description of the Prior Art The special characteristics of the hard, refractory ceramics gives rise to a wide range of applications which require hard, high-temperature strength, and wearresistant parts. Although there is a great deal of confusion and controversy surrounding the definition of ceramics, the term refractory ceramics" or ceramics as used herin includes refractory compounds of the carbides, borides, nitrides, and oxides. This is in accordance with the definition in Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Volume 4, page 774. The refractory ceramics can be classified according to their metal character: the compounds of the IVA-VIA periodic groups comprise the metallic ceramics, the most important of which are the cemented carbides of the refractory metals; the compounds of the IIIB-IVB periodic groups comprise the nonmetallic ceramics typified by the diamond-like carbides. The metallic or nonmetallic character significantly affects the manner in .which the hard, refractory ceramic can be joined to steel or other ferroalloy supports.

Some uses of'the hard, refractory ceramics are found in material finishing, sandblasting, and earth drilling operations. More specifically, hard ceramic tools are used to machine tough materials ranging from fiber glass to ferritic steel; hard carbide nozzles in sandblasting and earth drilling operations conduct highly abrasive fluids under extreme pressure conditions; and carbide inserts provide tough wear-resistant surfaces for earth drilling bits. In all of these applications, the ceramic members-blade, nozzle or insert-generally are formed in relatively small sizes which must be attached to a metal support for use. The metallic ceramics can be joined to metal supports by known brazing processes. Brazing is a welding technique for joining dissimilar metals and relies on the ability of a filler metal to wet both the ceramic and the metal base. When the filler metal solidifies, the parts are joined by a strong chemical bond; provided, of course, good wettability has been obtained. However, the ceramics are inherently difficult to wet by most filler metals. Moreover, the ceramic surface must be thoroughly cleaned. For hard ceramics, this usually requires grinding with a diamond wheel which adds to the cost of the operation. Thus in order to achieve a strong bond by brazing, extreme care must be exercised in the selection of the proper filler metal and in preparing the surface of the ceramic.

The nonmetallic ceramics are even more difficult to join to metal supports by conventional brazing techniques. Because of their, nonmetallic character, these ceramics are generally considered to be unwettable by conventional filler metals. Consequently, the hard, nonmetallic ceramics are usually mounted on the metal support by mechanical bonding techniques which utilize organic adhesives, clamping devices, or interference fits. The bond strength afforded by the first two of these techniques restrict the application of the hard, nonmetallic ceramics to relatively light service. They are entirely unsuited for mounting nozzles on earth drilling bits where the nozzles are subjected to differential pressures in the range of 10,000 to 15,000 psi. The organic adhesives and clamping devices are not capable of providing sufficient bond strength under these severe operating conditions. The interference fit requires finishing of the mating parts to a dimensional tolerance less than 0.005 inch. The high cost of finishing the hard ceramic articles to meet this close dimensional tolerance makes the interference fit technique uneconomical for most applications.

Another commonly used technique for joining hard, refractory ceramics and metal parts involves coating the ceramic with a film containing an active metal such as titanium or zirconium. The coating or film renders the ceramic part wettable by filler metals and permits the fabrication of the parts by conventional brazing processes. Unlike the present invention, these premetalizing techniques rely upon chemical bonding to effect the union of parts.

SUMMARY OF THE INVENTION The present invention provides an improved tool assembly which finds particular advantageous application in (1) devices used in sandblasting and earth drilling operations, and (2) cutting tools which can be used in lathes or other apparatus designed to process hard and tough materials.

Briefly the tool assembly comprises an outer ferroalloy support having an opening formed therein, a ceramic tool element positioned in the opening, and a filler metal containing finely divided refractory hard metal surrounding a portion of the tool element, the filler metal being brazed to the ferroalloy support and being mechanically bonded to the tool element. The tool assembly may be constructed by locating a shaped, hard, ceramic tool element concentrically in a suitable opening formed in a steel support; placing refractory hard metal powder in the opening in contact with the ceramic element and the steel support, infiltrating the refractory hard metal powder with a filler metal which wets the refractory hard metal and the steel support but not the ceramic element at an elevated temperature; and permitting the assembly to cool. As the assembly cools, the filler metal solidifies, bonding the refractory hard metal powder and the steel support into an integrated metallic sheath which surrounds the ceramic element. Further cooling causes the metallic sheath to contract about the ceramic element. Since the coefficient of thermal expansion for the metallic sheath is greater than that of the ceramic, the ceramic element is maintained in a residual state of compression at low temperature ranges. Laboratory tests show that the bonding strength afforded by this method is extremely high.

The hard ceramics capable of being mounted to steel supports include a class of materials which have become known in the art as hard nonmetallic materials which possess excellent properties of hardness, wear resistance, and high temperature strength. The hard nonmetallic ceramics include boron carbide (8 C), silicon carbide (SiC), beryllium carbide (Be c), sintered alumina (M boron nitride, cubic (BN), aluminum nitride (AIN), silicon nitride (si N and silicon boride (SiB Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Volume 4, page 74, prescuts the physical properties of the hard nonmetallic materials.

The type of ceramic used in a particular application will depend upon several factors including loading conditions, temperature, and type of service. In nozzle service, the diamond-like carbides (boron carbide and silicon carbide) are preferred because of their hardness and excellent wear-resistant properties. In the cutting tool application, the cutting blades can be composed of any of the nonmetallic ceramics, with the diamond-like carbides and sintered alumina being preferred. From the foregoing it is apparent that the diamond-like carbides and sintered alumina are of the greatest interest.

The ceramics can be shaped to the desired configuration by conventional hot pressing techniques which transform powdered nonmetallic material into a dense, self-bonded member usually in simple form such as a solid cylinder, hollow cylinder, disc, block, etc. A particularly advantageous feature of the present invention is that the ceramic element can be mounted on the metal support as is, requiring no additional finishing.

The filler metal can be any of the conventional brazing alloys capable of wetting the ferroalloy support and the refractory hard metal powder and having a liquidus below the melting point of the materials to be assembled. The particles can include any of the metallic refractories which are not metallurgically affected by the brazing temperature range (from about l,270 F to about 2,500 F). The refractory hard metals include the refractory metals (tungsten, columbium, molybdenum tantalum) and the heavy metal carbides, or mixtures thereof. The particle size should be small enough to provide capillary distribution of the molten filler metal during the infiltration phase of the process.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal, sectional view of an improved nozzle assembly constructed according to the present invention.

FIG. 2 is a longitudinal, sectional view of an improved cutting tool assembly constructed according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to two specific applications, e.g. nozzle assembly (FIG. 1) and a material-cutting tool (FIG. 2).

Referring to FIG. I, a nozzle assembly is seen to include a support sleeve 11 composed of steel or other ferroalloy. and a tubular, hard ceramic nozzle 12. The sleeve can be milled from a steel block to provide an internal cylindrical surface 13, an external threaded portion 14, and a hex head 15. The threaded portion 14 and hex head 15 permit attachment ofthe nozzle asembly 10 to the main tool body such as an earth-drilling bit or a sandblasting gun. Alternatively, the sleeve 11 can be provided with a welding flange, or the nozzle 12 can be mounted directly to the main tool body.

The ceramic nozzle 12 can be prepared by conventional hot pressing techniques which produce a dense, self-bonded member. In accordance with these techniques, the ceramic members are produced within a tolerance range of about 1 percent of a given dimension. The nozzle 12 can be in a variety of geometric shapes but preferably is in the form of a hollow cylinder. In this embodiment the nozzle 12 has a cylindrical outer surface 16 and an inner flow passage 17 provided with a tapered inlet 18. The composition and properties of some of the more important hard ceramics usable as nozzles are listed in Table I. The ceramic materials can include small amounts of impurities or materials added to enhance physical or mechanical properties of the finished member.

TABLE I Hard Ceramics Coefficient of H,, microhardness H,. Vickers hardness R,, Rockwell hardness (Scale A) In accordance with one aspect of this invention, the hard ceramic nozzle 12 can be mounted in the steel sleeve 11 wherein the bond is provided by a mechanical connection. The mounting process can be performed using conventional furnace brazing equipment. The outer periphery 16 of the nozzle 12 and the internal surface 13 of the sleeve 11 generally will be complementary shaped and circular in cross section so as to effect uniform distribution of forces. The sleeve 11 and nozzle 12 are placed in a refractory mold with the nozzle 12 being disposed concentrically in the sleeve 11 and with the complementary shaped portions arranged in confronting relation. The annular space 19 between the assembled parts should be large enough to permit the introduction of finely-divided refractory material. A clearance greater than about 0.010 inches is sufficient with clearances of at least 1/6 inch at least l/l6 inch being preferred.

Powdered refractory hard metal having a particle size between about and 400 mesh on the Tyler Standard Sieve Series is packed in the annular space 19. The interstitial flow passages in the packed interval provides for distribution of molten filler metal by capillary attraction. A powdered refractory metal (tungsten, molybdenum, columbium, tantalum, and their alloys) as well as a powdered hard metal carbide (one of the carbides of the IVA-VlA'periodic groups) can be used. The metal carbides are preferred, particularly tungsten carbide which possesses excellent mechanical properties and is readily wet by most filler metals.

The mold can be vibrated to settle the powdered refractory material and an excess can be placed above the annular space 19 in order to provide for the increase in annular space 19 resulting from the difference in thermal expansion of the metal sleeve 11 and the ceramic nozzle 12.

A solid filler metal can be preplaced in flow tubes provided in the mold and which discharge into the annular space 19. Suitable filler metals include the conventional brazing alloys capable of wetting the metallic refractory hard metal particles and the steel sleeve 11 and having a liquidus below the melting points of-the steel, refractory and ceramic materials. These include copper alloys, copper-zinc alloys, silver alloys, coppernickel alloys, copper-nickeLtin alloys, copper-nickeliron alloys, copper-cobalt-tin alloys, copper-nickelmanganese alloys, iron-nickelcarbon alloys, coppernickel-iron-tin alloys, and the like. Such alloys may contain minor quantities of other metals including zinc, tin, boron, beryllium, cadmium, silicon, manganese, and cobalt. From the foregoing it is apparent that there are a number of commercially available brazing alloys capable of wetting the ferroalloy and the refractory hard metal. Depending upon the type of ferroalloy, the type of refractory hard metal, and the contemplated tool service, some of the filler metals are preferred over others. In a preferred embodiment of the nozzle assembly comprising a sleeve of A18] 3310 steel, tungsten carbide particles, and a nonmetallic ceramic, the copper-nickel alloys are preferred. It should be observed that essentially all of the conventional filler metals are incapable of wetting the nonmetallic ceramics.

With the part 11 and 12 assembled and the materials properly positioned, the mold is placed in a furnace and the temperature increased to the brazing temperature of the materials used (from about l,270 F to about 2,500 F depending upon the composition of the filler metal). In some applications it may be necessary to select a filler metal having a high liquidus as experience has shown that best infiltration is achieved at the higher temperature range (from about 1,550 F to about 2,500 F). The filler metals can include materials to improve their wettability properties. At the elevated temperature, the tiller metal melts and by gravity flow and capillary attraction infiltrates the packed annulus 19. The molten filler metal substantially fills the pore space providing a continuous matrix in the annulus 19 and wets the individual refractory hard metal particles as well as the inner surface 13 of the steel sleeve 11.

At the elevated temperature, the metal sleeve 11 has expanded radially outwardly substantially more than radial expansion of the ceramic nozzle 12. The incremental increase in the annular space 19 is filled by the settling of the powdered refractory hard metal and by the molten filler metal. The elevated temperature is maintained until cmoplete infiltration is achieved. The mold is then permitted to cool. solidification of the filler metal provides a solid metallic intermediate structure which substantially fills the annular space 19, and which is coalesced to the internal surface 13 of the steel sleeve 11. The intermediate stucture comprises a matrix composed of the solidified filler metal and the refractory particles which lends mechanical strength to the sructure. Cooling of the mold and its contents from the solidus of the filler metal to room temperature causes the annular structure and metal sleeve 11 to contract about the ceramic nozzle 12 exerting a uniformly-distributed compressional force thereon. As mentioned previously, the molten filler metal exhibits properties of poor wettability on the hard ceramic because of the inherent incompatibility of the materials used. Consequently, the holding force is due principally to the compressional forces exerted by the intermediate metal structure and the steel sleeve 11. Microscopic physical embedment of the solidified filler metal in the outer surface 16 of nozzle 11 could also contribute to the surprisingly high bond strength afforded by the present invention.

Thus, the final nozzle assembly 10 is seen to include an outer ferro-alloy support 11, an inner hard, nonmetallic ceramic nozzle 12, and an intermediate structure brazed to the sleeve 11 and mechanically bonded to the nozzle 12 by an interference fit. The mechanical bond effected by the present invention relies on the difference in coefficients of thermal expansion between the refractory ceramics and the metallic materials. The nonmetallic ceramics have low coefficients of thermal expansion (range: 2.0 7.8 X l0' C) whereas the metallic materials have relatively high coefficients of thermal expanion (range: 10.0 19.0 X lO' C). During the cooling phase of the process, the contraction of the metallic materials imposes evenly distributed compressive forces on the cylindrical surface 16 of the nozzle 12. These compressive forces not only provide an extremely strong bond but hold the ceramic nozzles in a state of compression which significantly enhances the working strength of many of the ceramics, notably boron carbide.

Although any of the hard, nonmetallic ceramics can be used in the nozzle assembly 10, the diamond-like carbides (boron carbide and silicon carbide) are preferred because of their extreme hardness and their excellent wear-resistant propertie.

The following example illustrates the effectiveness of the present invention. High density, hot pressed boron carbide nozzles purchased from Norton company of Worcester, Mass, were mounted in a steel support sleeve by the procedure described above. Each of the nozzles were inch in diameter, A inch in length and had an inner opening of 3/32 inch. The steel sleeves, machined from AlSl 3310 steel, had an inside diameter of /2 inch, outside diameter of /1 inch, and a length of 1% inch. Tungsten carbide particles between 200 and 400 mesh size and a high-temperature filler metal were used to form the intermediate structure.

Erosion tests conducted on these nozzles revealed that they were far superior in erosion-resistant properties than were nozzle assemblies containing tungsten carbide inserts. The erosion tests were conducted by passing bentonitic drilling fluid containing varying amounts of silica sand through the nozzles at high velocities. Table ll compares the performance of sintered tungsten carbide nozzle assembly, cast tungsten carbide assembly, and boron carbide nozzle assembly.

Test data presented in Table ll indicates (l) boron carbide is more wear resistant than tungsten carbide in nozzle service, and (2) the bonding strength between the ceramic nozzle and metallic support is capable of withstanding high mechanical loads with no evidence of failure or leakage.

A section of one of the boron carbide nozzle assemblies was extracted to determine the nature of the bonding mechanism. A diamond saw was used to make two radial cuts about 120 apart in the nozzle assembly. The extracted pie-shaped portion thus was relieved of all compressional forces. The boron carbide fragment readily dislodged from the solidified filler metal indicating the absence ofa chemical bond. The filler metal, on the other hand, remained firmly affixed to the steel sleeve.

In regards to the application of the hard ceramics in cutting tools, considerable amount of difficulty has been experienced in mounting the non-metallic ceramic cutting blades to a metal holder. See Utilization of Ceramics for Metal Cutting Tools, by W. B. Kennedy, Rodman Process Laboratory, Watertown Arsenal, Report No. RPL6, United States Department of Commerce, Office of Technical Service FBI 1 l758. As pointed out in this report, it is extremely important that the cutting blade be firmly affixed to the holder to prevent vibrations which shorten the ceramic tool life. Cutting tools used in metal processing are subjected to relatively high operating temperatures (above 350 F). Therefore the mounting technique must be such to pro vide good bond strength at high temperatures.

Shown in FIG. 2 is a tool assembly 25 which can be adapted to metal cutting tools such as conventional lathes. As shown, the tool blade 26 composed of a hard ceramic has strength cylindrical body 27 and a shaped tip 28. The tip 28 can be shaped to the desired configuration by conventional diamond grinding techniques. The blade 26 is mounted in a steel sleeve 29 which can be milled from a steel block to provide an internal cylindrical surface 30, a threaded portion 31, and a hex head 32. The assembly 25 thus can be threadedly connected to a lathe or other cutting tool. The tool assembly 25 can be fabricated in the same manner described above for ceramic nozzle assemblies. The important ceramics which exhibit properties of extreme hardness, high-temperature strength, and wear resistance include alumina (Al O silicon carbide (SiC), and boron carbide (B C). However, other hard ceramics listed in Table I can also be used. The cutting tool 25 constructed according to the present invention can be used to process a wide range of materials.

These hard ceramics are available commercially in the form of high-density, self-bonded ceramics prepared by conventional hot pressing techniques.

We claim:

1. A tool assembly comprising an outer ferroalloy support having an opening formed therein; an inner tool element composed of a hard nonmetallic ceramic positioned concentrically in said opening; and a filler metal containing finely divided refractory hard metal brazed to said support and surrounding a portion of said tool element, said filler metal in the molten state having the ability to wet said ferroalloy support and said refractory hard metal but not said nonmetallic ceramic, said filler metal being bonded to said tool element by a mechanical interference fit.

2. The invention as recited in claim 1 wherein said tool element is a tubular nozzle having an outer periphery shaped complementary to said opening in said ferroalloy support.

3. The invention as recited in claim 2 wherein said opening and said nozzle are circular in cross section, said nozzle being sized in relation to said opening to provide a clearance of at least 0.010 inches between said outer periphery and said ferroalloy support.

4. The invention as recited in claim 3 wherein said refractory hard metal is tungsten carbide having a particle size between about and 400 mesh on the Tyler Standard Sieve Series.

5. The invention as recited in claim 1 wherein said nonmetallic ceramic is boron carbide.

6. A nozzle assembly for use in a drilling bit which comprises a ferroalloy support having an opening formed therein; a tubular nozzle of boron carbide positioned within said opening; and a filler metal containing finely divided hard metal carbide surrounding a portion of said nozzle and being brazed to said ferroalloy support, said filler metal in the molten state having the ability to wet said ferroalloy support and said hard metal carbide but not said boron carbide, said filler metal being bonded to said nozzle by a mechanical interference fit.

7. The invention as recited in claim 6 wherein said hard metal carbide is tungsten carbide having a particle size between about 100 and 400 mesh on the Tyler Standard Sieve Series.

8. The invention as recited in claim 7 wherein said support includes means for detachably mounting said nozzle assembly to said drilling bit. 

1. A tool assembly comprising an outer ferroalloy support having an opening formed therein; an inner tool element composed of a hard nonmetallic ceramic positioned concentrically in said opening; and a filler metal containing finely divided refractory hard metal brazed to said support and surrounding a portion of said tool element, said filler metal in the molten state having the ability to wet said ferroalloy support and said refractory hard metal but not said nonmetallic ceramic, said filler metal being bonded to said tool element by a mechanical interference fit.
 2. The invention as recited in claim 1 wherein said tool element is a tubular nozzle having an outer periphery shaped complementary to said opening in said ferroalloy support.
 3. The invention as recited in claim 2 wherein said opening and said nozzle are circular in cross section, said nozzle being sized in relation to said opening to provide a clearance of at least 0.010 inches between said outer periphery and said ferroalloy support.
 4. The invention as recited in claim 3 wherein said refractory hard metal is tungsten carbide having a particle size between about 100 and 400 mesh on the Tyler Standard Sieve Series.
 5. The invention as recited in claim 1 wherein said nonmetallic ceramic is boron carbide.
 6. A nozzle assembly for use in a drilling bit which comprises a ferroalloy support having an opening formed therein; a tubular nozzle of boron carbide positioned within said opening; and a filler metal containing finely divided hard metal carbide surrounding a portion of said nozzle and being brazed to said ferroalloy support, said filler metal in the molten state having the ability to wet said ferroalloy support and said hard metal carbide but not said boron carbide, said filler metal being bonded to said nozzle by a mechanical interference fit.
 7. The invention as recited in claim 6 wherein said hard metal carbide is tungsten carbide having a particle size between about 100 and 400 mesh on the Tyler Standard Sieve Series.
 8. The invention as recited in claim 7 wherein said support includes means for detachably mounting said nozzle assembly to said drilling bit. 